Conventionally, there has been known a fire detector configured to detect fire occurrence in a monitored area. The fire detector is equipped with a fire sensor configured to detect the concentration or temperature of smoke in the monitored area and a determination unit configured to compare a detection value of the fire sensor with a predetermined threshold and determine that fire has occurred in the monitored area, when the detection value of the fire sensor exceeds the predetermined threshold.
In fumigation fire that often occurs in an initial stage of fire, however, if fire occurs in which a relatively small amount of smoke is generated, in a conventional smoke-type fire detector that detects smoke, it takes a relatively long time until a detection value of the fire sensor exceeds a predetermined threshold, which may delay detection of occurrence of the fire.
Hence, in order to promptly detect fire occurrence, there has been proposed a combined type fire detector configured to correct a detection value of a smoke sensor based on the concentration of carbon monoxide gas in the monitored area and then use the value after correction to detect fire occurrence in a monitored area (See Patent Document 1, for example). This combined type fire detector is equipped with a smoke sensor configured to detect the concentration of smoke in the monitored area, a gas sensor configured to detect the concentration of carbon monoxide gas in the monitored area, and a determination unit configured to determine that fire has occurred in the monitored area. Then, for example, when a detection value of the gas sensor is greater than or equal to a predetermined value, the determination unit corrects the detection value of the smoke sensor by multiplying the detection value of the smoke sensor by a constant to increase the detection value of the smoke sensor, and determines that fire has occurred in the monitored area when the detection value after correction exceeds a predetermined threshold.